1. Field of the Invention
The present invention relates to an electron emission device and a method of manufacturing the same, and in particular, to an electron emission device having electron emission regions for emitting electrons and driving electrodes for controlling the electron emission.
2. Description of Related Art
Generally, electron emission devices are classified into a first type where a hot cathode is used as an electron emission source, and a second type where a cold cathode is used as the electron emission source.
Among the second type electron emission devices there are known the field emitter array (FEA) type, the surface conduction emission (SCE) type, the metal-insulator-metal (MIM) type, and the metal-insulator-semiconductor (MIS) type.
The electron emission devices are differentiated in their specific structure depending upon the type thereof, but basically have first and second substrates forming a vacuum vessel. Electron emission regions and driving electrodes are formed on the first substrate, and phosphor layers and an anode electrode are formed on the second substrate. With this structure, electrons are emitted from the electron emission regions toward the second substrate and excite the phosphor layers for making light emission or displaying desired images.
With the common FEA type electron emission device, cathode and gate electrodes are provided as the driving electrodes, and a focusing electrode is formed on the gate electrodes to focus the electron beams. In order to prevent the electrodes from being short circuited, first and second insulating layers are formed between the cathode and the gate electrodes and between the gate and the focusing electrodes, respectively.
In the conventional manufacturing of the above-structured FEA type electron emission device, the electrodes and the insulating layers are formed through only one process, taking into consideration simplified processing facilities and easy processing methodology. That is, the electrodes and the insulating layers are formed either through sputtering or vacuum deposition, or through screen-printing or laminating. For convenience, the former technique is called “thin filming,” and the latter technique is called “thick filming.”
When the electron emission device is completed utilizing only thin filming, the height difference between the electron emission regions and the focusing electrode is not so large as to heighten the electron beam focusing efficiency. Furthermore, when the electron emission regions are formed with thick filming, such as the screen-printing, the gate electrodes are placed at the plane lower than the electron emission regions so that it becomes difficult to control the electron emission, and the electron beams can be seriously diffused.
Accordingly, with the FEA type electron emission device, it has been preferable to form the insulating layer with a thickness of 1 μm or more. However, when the insulating layers with such a thickness are formed by thin filming, the stability and processing efficiency of the insulating layers deteriorates, making it difficult for mass production.
Furthermore, with the electron emission device completed through only thick filming, it is difficult to provide precise patterning, limiting the ability to make high resolution and high image quality devices.
Further, after the insulating layer is formed by thick filming, it is etched using wet etching to form opening portions. In this case, the electrodes formed on the insulating layer are used as an etching mask. That is, after the opening portions are formed at the focusing electrode, the second insulating layer is etched using the focusing electrode as an etching mask. After the opening portions are formed at the gate electrodes, the first insulating layer is etched using the gate electrodes as an etching mask.
However, since wet etching is made in an isotropic manner, the so-called undercut phenomenon, where the opening portions of the insulating layer are formed to be larger than those of the mask layer, is generated. Accordingly, the gate electrodes are partially suspended over the opening portions of the first insulating layer, and the focusing electrode is partially suspended over the opening portions of the second insulating layer, thereby deteriorating the shape stability of the electrodes.
Furthermore, when the insulating layer is formed by thick filming, it has a rough etching surface being the wall surface of the opening portions thereof so that the opening portions thereof have a rough plane shape. As a result, the opening portions of the gate electrodes and the focusing electrode formed on the insulating layer also have a rough plane shape proceeding along the shape of the opening portions of the insulating layer.
With the above-structured electron emission device, the electron emission characteristics become non-uniform due to the lower degree of shape precision of the electrodes and the insulating layers, and unintended discharge phenomenon and generation of leakage of current, make it difficult to form the device in a stable manner.